Conventionally, there is known a liquid-liquid contact device that provides countercurrent contact between a light liquid and a heavy liquid in order to generate interaction between the light liquid and the heavy liquid that has a larger specific gravity than the light liquid. The following Patent Literature 1 discloses an extraction device as one example of such a liquid-liquid contact device.
The extraction device disclosed in Patent Literature 1 provides countercurrent contact between a light-gravity liquid (light liquid) and a heavy-gravity liquid (heavy liquid) in order to generate extraction of a specific component from one of the light-gravity liquid and the heavy-gravity liquid to the other one as interaction. This extraction device of Patent Literature 1 has a double-tube structure having an outer tube extending in a vertical direction and an inner tube disposed in the outer tube to extend in the same direction as the outer tube. A space in an inside of the inner tube forms an inner chamber for providing countercurrent contact between the light-gravity liquid and the heavy-gravity liquid. An outer chamber is formed between an outer wall surface of the inner tube and an inner wall surface of the outer tube. A heavy-gravity liquid drawing-out hole that provides communication between the inner chamber and the outer chamber is formed at a lower part of the inner tube.
A light-gravity liquid supplying tube for supplying the light-gravity liquid to the inner chamber is disposed at a position that is in a lower part of the inner tube and that is above the heavy-gravity liquid drawing-out hole. A light-gravity liquid discharge tube that is in communication with the inner chamber so as to discharge the light-gravity liquid from the inner chamber is disposed at an upper part of the inner tube. A heavy-gravity liquid supplying tube for supplying the heavy-gravity liquid to the inner chamber is disposed at a position that is slightly above the light-gravity liquid discharge tube. A heavy-gravity liquid discharge tube that is in communication with the outer chamber so as to discharge the heavy-gravity liquid from the outer chamber is disposed at an upper part of the outer tube.
Further, the light-gravity liquid ejected from the light-gravity liquid supplying tube ascends in the inner chamber from below to above thereof while the heavy-gravity liquid ejected from the heavy-gravity liquid supplying tube descends in the inner chamber from above to below thereof, whereby the light-gravity liquid and the heavy-gravity liquid undergo countercurrent contact with each other in the inner chamber. This countercurrent contact allows a specific component to be extracted from one of the light-gravity liquid and the heavy-gravity liquid to the other one. The light-gravity liquid having made the countercurrent contact is discharged from an upper part of the inner chamber to an outside of the device through the light-gravity liquid discharge tube. Further, the heavy-gravity liquid having made the countercurrent contact flows out from a lower part of the inner chamber to the outer chamber through the heavy-gravity liquid drawing-out hole and ascends in the outer chamber to be discharged to the outside of the device through the heavy-gravity liquid discharge tube.
In the extraction device disclosed in Patent Literature 1, a phenomenon called flooding may occur in which, depending on conditions for supplying the light-gravity liquid and the heavy-gravity liquid into the inner chamber, the heavy-gravity liquid overflows out from an upper side of the inner chamber through the light-gravity liquid discharge tube, and the heavy-gravity liquid flows out to the outside of the device through the light-gravity liquid discharge tube that is originally designed to discharge the light-gravity liquid. For example, when a supply flow rate of the light-gravity liquid to the lower part of the inner chamber increases to be larger than a supply flow rate of the heavy-gravity liquid to the upper part of the inner chamber, the heavy-gravity liquid hardly descends from the upper part of the inner chamber due to a large amount of the light-gravity liquid that ascends from the lower part of the inner chamber and, as a result of this, the heavy-gravity liquid overflows to the outside of the device through the light-gravity liquid discharge tube connected to the upper part of the inner chamber. In such a case, the heavy-gravity liquid is discharged through the light-gravity liquid discharge tube originally designed in such a manner that only the light-gravity liquid is discharged in a state of being separated from the heavy-gravity liquid. This causes mingling of the light-gravity liquid and the heavy-gravity liquid with each other after processing in the extraction device, thereby necessitating a subsequent treatment of separating the light-gravity liquid and the heavy-gravity liquid from each other.